Broilers actually only live to be 9 weeks old, so their business cycle is very short. The old layers are labeled stew hens when you can find them at the store.
Broilers are different breeds than layers and “spent hens” tend to only get eaten by farmers, etc, because of the raised risk of deboning error and undesirably tough meat
I've heard they make excellent slow cook recipes like stew, soup, braise though :)
They apsolutely make excellent stock. I'm Hungarian and spent hen stock is quite commonky eaten in Hungary. Unfortunately spent hen is quite hard to source in the UK, where I am now.
Only if you live on a farm! Broilers are purpose-bred on a ridiculously fast timeline.